This invention relates to a matrix print head assembly of the general type disclosed in my prior U.S. Pat. No. 4,051,941, the disclosure of which is specifically incorporated herein by reference.
As disclosed in my prior U.S. Pat. Nos. 3,929,214, 3,994,381, and 4,051,941, various prior art armature retainer designs have been constructed and arranged to provide a spring means adapted to engage the radially outer end portion of the armature radially outwardly of the pivot on the outer edge of the outer pole for the stated purposes of (1) establishing a substantial moment of force on the armature causing pivotal movement toward the non-print position when the coil is de-energized, (2) maintaining the armature in engagement with the outer pole to insure a proper magnetic flux path therebetween, and (3) providing an adjustable reference armature abutment surface or surfaces by which the air gaps between the armatures and the inner pole may be more or less uniformly controlled.
A disadvantage of such prior arrangements is that the moment of force exerted by the spring means on the outer end of the armature opposes the wire driving movement of the armature from the non-print position toward the print position. In addition, the moment of force increases during such movement. As a result, the frequency response of the armature is reduced. I have discovered that provision of such a moment of force is not only undesireable but also unnecessary with use of the construction and arrangement of the present invention. Furthermore, by use of the present invention it is not necessary to maintain the armature in contact with the pole pivot for the purpose of insuring a proper magnetic flux path therebetween although it is possible if desireable to provide light force holding means, engageable with the armature directly opposite the pole pivot so as to eliminate the prior art moment of force, for the purpose of reducing armature vibration with reduction of resulting wear and noise in operation. The desired uniformity of the air gaps between the armatures and their associated inner pole portions is maintained in the present invention by a construction and arrangement wherein an armature retaining cover means has (1) axially facing pole abutment surfaces located in a common radially plane substantially coplanar with pole end surfaces also located in a common radially plane, (2) precisely located armature confining surfaces on the armature retaining cover means to define, in conjunction with the pole end surfaces, relatively precisely dimensioned and located armature confining slot means. In the presently preferred embodiment, the pole end surfaces are lightly ground after assembly to establish the desired coplanar relationship and the side surfaces of the armatures are also ground prior to assembly to assure parallelism between those surfaces.
An object of the present invention is to provide new and improved armature retainer means for retaining the armatures of a matrix print head assembly solely by pivotally supporting the outer end portions of the armatures on the outer edges of the outer poles and closely but loosely confining a narrow length portion of the armatures by confining slot means defined by an axially extending rim portion of the retainer plate which rigidly abuts the outer pole, with or without use of any resilient armature biasing means, and with the inner end portions of the armatures being located in the non-print position only by the spring biased wire drive heads. If a resilient armature biasing means is used, it engages the armature directly opposite the pole pivot with a low spring force sufficient only to lightly hold the armature on the pivot without application of any moment of force opposing the movement of the armature from the non-print position to the print position. The resilient armature biasing means are in the form of individual compression springs mounted in the retainer plate or individual integral tongue portions or individual integral bearing rib portions. Dampening means may be provided opposite both the radially innermost and radially outermost portions of the armature.
Another object is to provide new and improved wire guide means for guiding the wires by use of only one elongated guide end bearing member centrally mounted in the wire housing cavity and only one end bearing member mounted on the end wall of the wire housing with wire guide means integrally formed in the end wall of the wire housing axially adjacent the end bearing member.
Another object is to provide new and improved pole mounting means for mounting the pole members on the pole support plate by press fitting an enlarged base portion of the pole members into smaller size openings in the pole support plate defined by an annular rib and opposite enlarged counter bores causing flow of pole member material around the annular rib and into the counterbore to form a locking annular groove about the annular rib.
Other objects and advantages of the present invention are reduction of number of parts, reduction of cost of manufacture, elimination of adjustment devices, elimination of parts subject to wear and replacement, simplification assembly, and repair and replacement of parts.